Superluminal propagation in resonant dissipative media

We analyse the superluminal propagation of optical narrow-band pulses at resonances in dissipative media. We find that, for a broad class of optical systems holding this type of lossy faster-than-light transmission capability, the output waveform is an attenuated, time-advanced version of the input which can be interpreted as the result of the interference of two scaled replicas of the input having a positive relative delay. This analysis is shown to apply, among other scenarios, both in the propagation in a passive bulk medium at an electronic resonance and in a dielectric waveguide coupled to a lossy micro-ring resonator.